Portugal is definetly the European country with most genetic contribution from black slaves. Check this interesting table:
In the locality of Alcácer do Sal, Portugal, African lineages reach 28% of the population!!
In the entire Portugal, African lineages are never below 3%, being more prevalent in Madeira (16.8%) and in the South (around 11%), where African slaves were mostly introduced.
I dont know how that African impact influenced the Portuguese phenotype. In Lisbon I was surprised, because native Portuguese look "whiter" than I expected, but I did see some "Mulattoid" types, but I dont know if they were Portuguese: they could be Brazilians or Africans.
I've never been to Madeira, but I saw some people from Madeira on television and some of them looked "suspect"